<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>子代选择器</title>
		<script src="js/jquery-3.3.1.min.js" type="text/javascript" charset="utf-8"></script>
	</head>
	<body>
		<ul id="test">
			<li>li_1</li>
			<li>li_2</li>
			<li>li_3
			<ul>
				<li>li_3_1</li>
				<li>li_3_2</li>
				<li>li_3_3</li>
			</ul>
			</li>
		</ul>
	</body>
</html>

<script type="text/javascript">
	$("#test>li").css("border","2px solid red")
</script>
